Investigation of Basalt and Pyroxene Oxidation
The surface of Venus should be extensively altered by interactions with its CO2-CO-SO2 atmosphere, which is at ~95.6 bars and ~470°C at the surface [1,2]. These gas-solid interactions should include oxidation and sulphurisation, which produce thin coatings of magnetite, hematite, and/or sulphates on the surfaces of minerals and rocks [3]. Previous studies have examined the effect of high-temperature oxidation of ferromagnesian silicate minerals on visible to nearinfrared (VNIR) spectrum [e.g. 4], but these experiments have used various elevated temperatures with short duration runs. Hence, here we look to isolate oxidation effects on diagnostic pyroxene absorption bands at a stable elevated temperature for longer durations. The subsequent changes in the spectrum enables constraints for estimates of pyroxene and basalt weathering rates to be determined. Pyroxenes, ferromagnesian silicate minerals, are abundant in terrestrial basalts, and thus should be a major constituent of Venus basalts [5,6]. In VNIR, pyroxenes exhibit distinctive absorption bands near the 1 and 2 µm wavelengths; both arise from Fe2+ crystal field (CF) transitions [7]. One of these absorption bands may be visible from space as Venus’ surface is visible through three spectral “windows” at 1.01, 1.10 and 1.18 µm, which were recognised and used by Venus Express’ Virtual Infrared Thermal Imaging Spectrometer (VIRTIS) [8]. Using VIRTIS and Venus Express data on light emitted by Venus’ surface in these bands, [9] identified ‘hotspot’ regions with anomalously high emissivity (or low reflectance). These ‘hotspots’ were suggested to be fresh, unweathered basalt flows, implying that the flows are young, perhaps less than 250,000 years old. Our previous work [10] indicates that these flows may be only a few years old, but that result is based only on the oxidation of olivine and not other basaltic minerals. This study extends [10] by investigating weathering rates of pyroxene and a terrestrial basalt analog, discerning the effects of oxidation on VNIR spectra of pyroxene and basalt, and testing implications for volcanism on Venus.
Authors: K.S. Cutler, J. Filiberto, A.H. Treiman and D. Trang
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